1. Field of the invention
The present invention relates to a method of performing optical proximity corrections (OPC) of a photo mask pattern, and more particularity, to a method of performing OPC to rapidly correct a photo mask pattern by using computer to eliminate an optic proximity effect.
2. Description of the Prior Art
In the semiconductor process, in order to transfer an integrated circuit pattern onto a semiconductor wafer, a photo mask pattern is designed first. Then a photo mask is formed according to the photo mask pattern by performing a photolithographic process. The pattern on the photo mask is then transferred in proportion onto a photo-resist layer on a semiconductor wafer.
The critical dimension of the pattern on the photo mask is limited by the resolution limit of the optical exposure tool. As the design pattern of integrated circuits becomes smaller and the photo mask pattern becomes of higher density in its pattern arrangement, the optical proximity effect will easily occur during the photolithographic process for forming the photo mask according to the photo mast pattern. The optical proximity effect will cause overexposure or underexposure at corners in the photo mask pattern, resulting in a resolution loss which causes formations of round profiles at those corners or so-called corner rounding effect. Moreover, when the pattern is transferred onto the photo-resist layer during the photolithographic process, same effects occur, resulting in variations in the patterns on the photo mask and on the photo-resist layer. Therefore, the pattern on the photo-resist layer is far different from the original photo mask pattern.
The prior art method to solve the above problem is to perform optical proximity corrections (OPC) of a photo mask pattern by using a computer aided design (CAD), so that a corrected pattern is formed on the photo mask to eliminate the optical proximity effect.
Please refer to FIG. 1 to FIG. 4. FIG. 1 to FIG. 4 are schematic diagrams of a prior art method for performing optical proximity corrections of a photo mask pattern by using a computer. In the prior art method, the OPC is performed on a photo mask pattern 10 by using a computer (not shown). The memory of the computer can be used for storing the photo mask pattern 10 and programs, and the processor of the computer can be used for executing the programs stored in the memory.
As shown in FIG. 1, the photo mask pattern 10 comprises a plurality of sides and corners, and each corner formed by joining two adjacent sides. The prior art method for performing OPC of the photo mask pattern 10 is to find the places which may be affected by an optic proximity effect according to a predetermined design rules checker. In addition, as the photo mask pattern 10 is affected by the optic proximity effect, it becomes round in shape. In the prior art method, this condition is simulated to form a simulation pattern 12 of a round shape as shown in FIG. 2. Finally, dark corners 14 outside the simulation pattern 12 are found by comparing the photo mask pattern 10 and the simulation pattern 12, as shown in FIG. 3. The dark corners 14 are the regions where resolution loss may possibly occur. In FIG. 3, the regions labelled by oblique lines illustrate the dark corners 14.
After finding the regions where resolution lossmay possiblly occur, a protruded portion 16 of a rectangular shape is formed at each dark corner 14 as a serif to prevent the dark corner 14 from being affected by the corner rounding effect. As shown in FIG. 4, the protruded portions 16 and the photo mask pattern 10 are combined to form a photo mask pattern 18 with OPC in which the optical proximity effect is eliminated. However, the prior art method for performing OPC of the whole photo mask pattern 10 takes more than 24 hours to perform the method. It is a large waste in the process cost.
It is therefore a primary objective of the present invention to provide a method of performing optical proximity corrections (OPC) of a photo mask pattern by using a computer to solve the above mentioned problem.
In a preferred embodiment, the present invention provides a method of performing optical proximity corrections of a photo mask pattern by using a computer. The computer comprises a memory for storing the photo mask pattern and programs, and a processor for executing the programs stored in the memory. The photo mask pattern is formed on a photo mask which is used when performing a photolithographic process for forming a predetermined original pattern by exposing a photo-resist layer in a predetermined area of a semiconductor wafer. The method comprises:
dividing the photo mask pattern into a plurality of rectangular blocks, each of the rectangular blocks comprising four sides and four corners each formed by joining two adjacent sides wherein each rectangular block can be a bright rectangular block or a dark rectangular block, at least one side and two corners of the rectangular block are shared with another rectangular block;
checking each of shared corners of the photo mask pattern to find corners which may be affected by an optic proximity effect; and
modifying the corners which may be affected so as to prevent them from being affected by the optic proximity effect.
It is an advantage of the present invention that the method of performing OPC of a photo mask pattern by using computer can rapidly and effectively correct the photo mask pattern to eliminate the optic proximity effect.
This and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment which is illustrated in the various figures and drawings.